Process for removal of dirt from pulp



' y 9, 1940- v. FORMAN 2,207,213

PROCESS FOR REMOVAL OF DIRT FROM PULP Filed Aug. 6, 1937 2 Sheets-Sheet 1 INVENTOR. lo/ei/v M fmmw M --U' ATTORNEY? July 9, 1940. v FQRMAN 2,297,218

PROCESS FOR REMOVAL OF DIRT FROM PULP Filed Aug. 6, 1937 I 2 Sheets-Sheet 2 l l \Ldj 1 42% l I 11 i? n? TY H Z J: 1J1 33 l INVENTOR. [aeav K/Z /WW 9 BY M.%

ATTORNEYS I Patented July 9, 1940 UNITED STATES rnocess ron REMOVAL or mar FROM PULP Loren V. Forman, Munising, Mich., assignor of one-half to The Munising Paper Company, Munising, Mich., a. corporation of Ohio Application August a, 1937, Serial No. 157,767

1 Glaim.

This invention relates to a process for the removal of dirt from pulp for making paper.

It is the object of this invention to provide a novel process for the separation of dirt from 5 paper pulp by hydraulic classification. In the definition of dirt" there is included rust, scale, sand, mineral dirt, particles of digester lining, lime particles, knots, uncooked chips, bark specks, shives and fiber bundles. All suspended material except the individual pulp fibers is classified as dirt.

It is an object of this invention to utilizelow consistencies of paper pulp in which sufiicient 'difierentials in settling rates are secured between dirt and pulp to provide a basis for separation.

It is an object of the invention to utilize a uniform velocity of a rising water column at such speed as to prevent fibers from passing downwardly into a receiver, yet permitting dirt to fall into the receiver so thatby a carefully controlled I0 or without continuous means for discharge therefrom. I

It is an object of this processtodilute the pulp to the proper consistency followed by' a combination of rifliing sedimentation and hydraubodies from the cellulosic fibers. p g

It is an object to provide this process so that :5 lie classification to secureseparation of all foreign it is applicable toall types-'of pulp and at any points in the systemfrom the-digester's' to the to paper machines.

It is a further'object to'provide forthe addi tion to the foregoing a process of the use of I seeis utilized.-

maximum consistency above which no,settling is possible and. no removal can be accomplished. It -,is an object of rthis, invention to employ,

consistencies that arerelatively' low .sO that. foreign materialsheietofore' notv commonly classified as dirt and not considered removable by hyqraul'i I 5 classification can be removed. It hasjbeen found; when practicing the teachings of this invention, t pmm p e me c a ifie a an i e n a ge bf 29- Per en i ,v .25 e cent and from 0.02 per cent-up. "Consistency is defined as pounds of fiber in one hundred pounds of the suspension consisting of water, fibers and/or other material suspended in it.

It is an object of this invention to provide for actual separation of dirt from fibers in the classifier at consistencies from zero to that'at 5 which the pulp is introduced into the classifier.

It is a further object to reduce the cost of wood as hereinafter explained.

Referring to the drawings:

Figure 1 is a diagrammatic view in side elevationof the apparatus for the practice ofthis invention as applied to a rifller channel.

Figure 2 is a section on the line 2-2 of Figure 1, looking in the direction of the arrows.

Figure 3 is a view similar to Figure 1 showing 5 a modified form for the introduction of secondary water and for the practice of stepwise classification in the hopper prior to final classification in the sorting column.

Figure '4 is a top plan view thereof.

Referring to the drawings in detail, I designates the inlet of stock pulp and dirt'pajssing through the horizontally disposed channel 2 of a riflier. 3 indicates the level of the stock. The

bottom of this rifiier channel 2 is providedwith one or more hoppers 4. The, region of entry of the dirty stock is in the zone designated generally at 5. At this point the dirty stock enters in the pyramidal or conical hopper 4. AS the dirtystock passes from the channel 2 into m this region',.5,.its forward-velocity decreasesdue' to an enlarging cross section of the body of stock as it passes over and into the hopper 4. At the same time the heavier particles settle toward the bottom of ,the. hopper .4 and then enter the sort-.

ing column 6- whichis of restricted cylindrical area and communicateswith thebottom of the hopperl." i In this sorting columnfi is introducedga rising, currentof water through the gpipe. 'l which equipped with' a suitable -co ntro l-; valve. This,

. Qwater is introduced, referabl tan entiall to! ondary water and means of 'giving 'stepwise p classification priorv to theifinal classification in 5 the sorting column in which the foregoing process=* sorting 1m. 6. ;Its motion. is. relatively very,

secure enough spiralmotion to produce a uniform rising. currentqu across the -.cross ,jSeCtilQ of .the

It is the object ofthiswinvention mapp1yeth mt pmduce any separatm y discovery that for each typeiofdirt, there-is-az.

centrifugal force. The amount of water addedais carefully; regulate'dso that-l no;goodrfiberswillq settle, yetxany material having a highensettling velocity than: the :goodfibers .will settle through terial' is introduced through lthe hopper: S-Jahd-F- past the valve control H1. The dirt so deposited in the rec iver 8' may be intermittently' or {con- 5 timi'ously conveyed away. There' are' no' currents The-settlingrates of'thedirt' matenaisare-aa I 1-;

termined as a function of the consistency of the o0 pulp suspension. It has been found that by going to low consistencies suflicient difierentials in settling rates between the dirt and pulp are obtained to serve as a basis for separation. The amount of water introduced into the sorting column or settling tube 6 is just sufiicient to prevent fibers from passing down into the receiver, yet

not too great a flow to permit dirt to fall through it into the receiver 8.

This process results in the dirt-free pulp making its exit as clean stock through the region generally designated II at the top of the outgoing side of the hopper 4 into the continuation of the rifller 2. This process has been found to work very satisfactorily as a knotter, possessing several advantages over the rotating cylindrical knot screens used in this art.

It is also optional to use baflies in the rifiier channel I above the classifier hopper 4 to deflect the pulp stream downwardly into the classifier. These baflies la may extend downwardly into the upper portion of the hopper, or where the classifiers are used independently, they may be located in the upper portion of the hopper. .One of the preferable locations is indicated in Figures 1 and 2.

The method of introducing and removing pulp from the classifier, of course, can be employed in the case of a conical hopper operated independently of a rifller. In that event, the pulp is introduced centrally either at the surface, or at some submerged point along the axis of the cone, in such a way that the direction of flow at the point of introduction is radial at that section. In such a case the clean stock overflows the top circumference of the cone and is collected and carried away in a circular trough or launder.

Referring to Figures 1 and 2, the valve I I! is wide open during normal operation. If a single receiver 8 is used, the valve Ill is closed tightly momentarily while the receiver is emptied and immediately opened wide when normal operation is resumed. When two receivers are provided and operated so that one is emptied while the other fills, an additional swing gate is provided to divert the dirt to the proper receiver and seal off the other for emptying. In this case, as when continuous removal of dirt from the receiver is used, the valve I0 is merely an emergency valve to permit repairs to the receiver without loss of pulp. For intermittent operation of a single receiver, the piping connections have been drawn schematically as indicated on Figure 2 by the legends. To empty the receiver, valve I0 is closed, the discharge valve is opened, the water valve is opened to wash out the dirt, and the air vent is opened. When the dirt has all washed out, the discharge valve is closed and the water valve and air vent closed after the receiver is full.

of water, whereupon valve I0 is reopened.

This classifier has the advantage of being able to separate small particles of heavy dirt which ordinarily pass through a knot screen easily and may pass through the fiat screens if the particle size has been sufficiently reduced by the time it reaches that point in the system. There is no fiber loss in the classifier as each knot or dirt particle is washed free of stock as it falls into the settling column 6 against the rising current of water.

Another advantage of this classifier process for removing knots is that there is no tumbling about of the knots as in the screen type knotter which tends to break up bark dirt and some knots, thereby producing small fragments which are very difllcult to remove in subsequent operations.

By carefully controlling the rising current from the pipe 1 in the column 6, a very efiicient removal of fine dirt is obtained so that when the classifier is used in series with a rifiler there is produced a cleaner pulp than the conventional rifiler and fine screen in series. A microscopic study has revealed that much of the fine dirt can pass through fine screen slots more easily than can the fibers themselves. The minute specks of high density dirt, which usually have quite regular shapes, are not removable by screening when their smallest dimension is less than the width of the screen slot, yet they are readily removed by the classifier.

The fine wood dirt particles having settling velocities very close to those of fibers are most difiicult to remove by classification, yet this process removes this material efiiciently even in the size range encountered in stock that has already passed a ten cut screen plate. This method of removal of this process does not possess the disadvantage encountered in vibrating fiat screens to break up brittle, friable dirt to the point where it passes through the slot into the system.

This classifier process has a distinct advantage over fiat screens in the cost of operation and maintenance. It has been found that when the classifiers and rifilers are combined, utilizing the rifller area as the primary settling chamber and equipping the riflling lines with the hopper bottoms and sorting columns of this invention for continuous separation and removal of knots and dirt, it is possible to get the resultdescribed herein.

This process does not employ the centrifugal principle in any way. The only reason for a rotating of the sorting column to any degree is to secure a uniform distribution of the water so that there will be a uniform vertical current at all points in the cross section of the sorting column 6.

This process permits of the further advantage that it permits of continuous operation as distinguished from intermittent operations of present riflling processes. The present process provides for positive separation of dirt from fibers which eliminates stock losses. It permits of the removal of finer material thanis generally included in the ordinary definition of dirt.

Turning to the form shown in Figures 3 and 4, the hopper 4 is provided with a plurality of spaced collars I2 crimped to conform with the inside of the hopper and having projecting edges l2a, as shown in Figure 4, of sheet metal, steel plate, or other suitable material which are fastened in place in planes approximately parallel to the top of the conical or pyramidal hopper 4. The collars are made in sections of a cone or pyramid depending upon the shape of the classifier hopper 4, so that the separated material will slide down over the upper surface of each collar l2 rather than deposit upon it.

The secondary water is distributed through shower pipes built in either square or circular shape to fit under the respective collars l2. These pipes are indicated l3 and are fed by supply pipes I 4 equipped with suitable control valve. The secondary water so delivered is relatively small in volume and will serve to reduce the consistency of the body of pulp and dirt and provide an upward sorting current in the regions of restricted cross section formed by the collars l2, particularly where the pulp slides down the collars l2 and ofi the edges l2a.

With the proper adjustment of the secondary water, stepwise classification is obtained which is more efficient in many cases than classification by the one sorting column 6 alone. Especially where a cone shaped hopper is used, the cross section is restricted by a fiat wheel or a ring with spokes instead of the ring alone.

Another variation of the apparatus for practicing this process is the use of perforated plates having thearea of perforations suitably less than the total cross sectional area.

consistencies The primary basis upon which this process has been developed was the discovery that for each type of dirt there is a maximum consistency above which no settling is possible and no removal can be accomplished. At the present time it is understood that consistencies of 0.3 per cent to 0.5 per cent are used in connection with the separation of dirt, but these consistencies will not permit of the separation of material not commonly classified as dirt but which are very injurious if they remain in the paper pulp. It is possible by the employment of this process to utilize consistencies below this range, which results in removing smaller foreign materials heretofore not commonly classed as dirt and not considered removable.

Preferably this invention has been practiced by supplying pulp to the classifier at consistencies of from 0.1 per cent to 0.25 per cent, but consistencies from 0.02 per cent up are feasible. Furthermore, within the classifier the consistency becomes progressively lower toward the bottom of the hopper 4. This is due to the addition of secondary water through the pipes I3 and the water from the pipe I delivered to the sorting column. At the bottom of the sorting column 6', a complete separation of fibers and dirt has been accomplished and hence the consistency at that point is zero. Consistency is defined as pounds of fiber in one hundred pounds of the suspension consisting of water, fibers and/or other materials suspended in it.

Actual separation of dirt from fibers in the classifier takes place at consistencies from zero on up to that at which the pulp is introduced into the classifier.

Efiect on the preparation of the wood for cooking The result of this invention in being able to remove all types of dirt, including bark specks, from the cooked pulp makes possible the complete elimination, or at least a material reduction,

. in the amount of mechanical cleaning done in knot borers, splitters, barking drums, etc.

The latter often amounts to five or ten mills making fine paper paying premium prices for clean wood.

It is further possible through the use of this process to cook unbarked wood which eliminates the barking process in mills which do their own barking and eliminates the expense of buying peeled wood where that is practiced.

It is further possible by this process to reduce wood and bark to pulp form, reduce the pulp and associated materials suspended in the water to the consistencies indicated and to make the elimination by this hydraulic classification process of all of the foreign material without going to the expense of pre-preparing the raw material by the expensive methods heretofore practiced, particularly in the making of fine papers.

There are two other important applications of this process. The first is merely a refinement in the use of the classifier in conjunction with a rifller in which instead of equipping the entire length of a riffler channel with a series of hopper bottoms and classifiers, only one unit is installed, probably but not necessarily at the discharge end of the channel, and. the dirt settled in other portions of the channel delivered to it for final separation from adhering pulp. This settled material may be delivered to the classifier by any type of mechanical conveyor, such as a slow movin drag scraper conveyor or screw conveyor, or by pneumatic or hydraulic means.

The other application is the use ,of this classifier to separate clean pulp from dirt in the rejects from any pulp screening operation. Such rejects, usually known as tailings or screenings, commonly are rich in dirt, containing as a rule less pulp than dirt. However, if the clean pulp is not reclaimed from the rejects, the economic loss is considerable. Likewise, in cases Where the conventional type of rifflers are used and cleaned intermittently, this classifier can be employed to operate on the settled material as it is washed out to free it of clean pulp.

It will be understood that the term riffler in its broadest sense includes not only the conventional type consisting of channels containing numerous bafiies over which the pulp must flow, but all types of settling channels and basins, whether containing several baflles, few baflies, or no baflles at all.

It will be understood that I desire to comprehend within my invention such modifications as come within the scope of the claim and the invention.

Having thus fully described my invention what I claim as new and desire to secure by Letters Patent is:

The process of separating dirt from wood pulp in a water suspension, which comprises diluting the stock to a consistency 'of .02% to" 25%, flowing .said suspension in a horizontal plane across a settling chamber, allowing the dirt and heavy 

